You need to get it programmed. The theft deterrent is likely locking you out. I don't know why you changed it in the first place but you still may have another problem that the computer didn't fix also.

Hi guys. Let me butt in and add a tidbit. If your van has the factory anti-theft system, use the key to turn the lock cylinder in the lift gate. That will program the Engine and / or Body Computer to work with the anti-theft system and allow the engine to run. If your van doesn't have the factory anti-theft system and you installed a used Engine Computer with that programming, it can't be "unprogrammed". You have to use a computer from another van that did not have anti-theft programming.

When it's in theft mode, the engine will typically run for just two seconds, then stall.